| Message ID | 20201002172559.4000748-4-guro@fb.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: allow mapping accounted kernel pages to userspace | expand |
On Fri, Oct 02, 2020 at 10:25:58AM -0700, Roman Gushchin wrote: > The lowest bit in page->memcg_data is used to distinguish between > struct memory_cgroup pointer and a pointer to a objcgs array. > All checks and modifications of this bit are open-coded. > > Let's formalize it using page memcg flags, defined in enum > page_memcg_data_flags. > > Additional flags might be added later. > > Signed-off-by: Roman Gushchin <guro@fb.com> > Reviewed-by: Shakeel Butt <shakeelb@google.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
On Fri 02-10-20 10:25:58, Roman Gushchin wrote: > The lowest bit in page->memcg_data is used to distinguish between > struct memory_cgroup pointer and a pointer to a objcgs array. > All checks and modifications of this bit are open-coded. > > Let's formalize it using page memcg flags, defined in enum > page_memcg_data_flags. > > Additional flags might be added later. > > Signed-off-by: Roman Gushchin <guro@fb.com> > Reviewed-by: Shakeel Butt <shakeelb@google.com> Acked-by: Michal Hocko <mhocko@suse.com> > --- > include/linux/memcontrol.h | 32 ++++++++++++++++++++------------ > 1 file changed, 20 insertions(+), 12 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index c7ac0a5b8989..99a4841d658b 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -343,6 +343,15 @@ struct mem_cgroup { > > extern struct mem_cgroup *root_mem_cgroup; > > +enum page_memcg_data_flags { > + /* page->memcg_data is a pointer to an objcgs vector */ > + MEMCG_DATA_OBJCGS = (1UL << 0), > + /* the next bit after the last actual flag */ > + __NR_MEMCG_DATA_FLAGS = (1UL << 1), > +}; > + > +#define MEMCG_DATA_FLAGS_MASK (__NR_MEMCG_DATA_FLAGS - 1) > + > /* > * page_memcg - get the memory cgroup associated with a page > * @page: a pointer to the page struct > @@ -404,13 +413,7 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page) > */ > unsigned long memcg_data = READ_ONCE(page->memcg_data); > > - /* > - * The lowest bit set means that memcg isn't a valid > - * memcg pointer, but a obj_cgroups pointer. > - * In this case the page is shared and doesn't belong > - * to any specific memory cgroup. > - */ > - if (memcg_data & 0x1UL) > + if (memcg_data & MEMCG_DATA_OBJCGS) > return NULL; > > return (struct mem_cgroup *)memcg_data; > @@ -429,7 +432,11 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page) > */ > static inline struct obj_cgroup **page_objcgs(struct page *page) > { > - return (struct obj_cgroup **)(READ_ONCE(page->memcg_data) & ~0x1UL); > + unsigned long memcg_data = READ_ONCE(page->memcg_data); > + > + VM_BUG_ON_PAGE(memcg_data && !(memcg_data & MEMCG_DATA_OBJCGS), page); > + > + return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); > } > > /* > @@ -444,10 +451,10 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page) > { > unsigned long memcg_data = READ_ONCE(page->memcg_data); > > - if (memcg_data && (memcg_data & 0x1UL)) > - return (struct obj_cgroup **)(memcg_data & ~0x1UL); > + if (!memcg_data || !(memcg_data & MEMCG_DATA_OBJCGS)) > + return NULL; > > - return NULL; > + return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); > } > > /* > @@ -460,7 +467,8 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page) > static inline bool set_page_objcgs(struct page *page, > struct obj_cgroup **objcgs) > { > - return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | 0x1UL); > + return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | > + MEMCG_DATA_OBJCGS); > } > #else > static inline struct obj_cgroup **page_objcgs(struct page *page) > -- > 2.26.2
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index c7ac0a5b8989..99a4841d658b 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -343,6 +343,15 @@ struct mem_cgroup { extern struct mem_cgroup *root_mem_cgroup; +enum page_memcg_data_flags { + /* page->memcg_data is a pointer to an objcgs vector */ + MEMCG_DATA_OBJCGS = (1UL << 0), + /* the next bit after the last actual flag */ + __NR_MEMCG_DATA_FLAGS = (1UL << 1), +}; + +#define MEMCG_DATA_FLAGS_MASK (__NR_MEMCG_DATA_FLAGS - 1) + /* * page_memcg - get the memory cgroup associated with a page * @page: a pointer to the page struct @@ -404,13 +413,7 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page) */ unsigned long memcg_data = READ_ONCE(page->memcg_data); - /* - * The lowest bit set means that memcg isn't a valid - * memcg pointer, but a obj_cgroups pointer. - * In this case the page is shared and doesn't belong - * to any specific memory cgroup. - */ - if (memcg_data & 0x1UL) + if (memcg_data & MEMCG_DATA_OBJCGS) return NULL; return (struct mem_cgroup *)memcg_data; @@ -429,7 +432,11 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page) */ static inline struct obj_cgroup **page_objcgs(struct page *page) { - return (struct obj_cgroup **)(READ_ONCE(page->memcg_data) & ~0x1UL); + unsigned long memcg_data = READ_ONCE(page->memcg_data); + + VM_BUG_ON_PAGE(memcg_data && !(memcg_data & MEMCG_DATA_OBJCGS), page); + + return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); } /* @@ -444,10 +451,10 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page) { unsigned long memcg_data = READ_ONCE(page->memcg_data); - if (memcg_data && (memcg_data & 0x1UL)) - return (struct obj_cgroup **)(memcg_data & ~0x1UL); + if (!memcg_data || !(memcg_data & MEMCG_DATA_OBJCGS)) + return NULL; - return NULL; + return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); } /* @@ -460,7 +467,8 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page) static inline bool set_page_objcgs(struct page *page, struct obj_cgroup **objcgs) { - return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | 0x1UL); + return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | + MEMCG_DATA_OBJCGS); } #else static inline struct obj_cgroup **page_objcgs(struct page *page)